Ok, I was going to Sanctuary to switch McReady for Curie, when I got an alert "The Castle is under attack". McReady and I fast traveled to the castle. After the loading screen, we were met buy 10 Institute synths (which sealed the Institute's fate, HELLOO BoS!). My settler count was 14, but I lost 1. Killed the synths, dragged and placed their bodies by the front door as a warning. Paid respects to the lost settler, fixed the damaged crops, and sold Ronnie the salvage from the Synths. I looked at my quests and saw "Help the Castle!".... What? I just did that! I can't move (tested), because I'll fail and lose 8 more settlers... So wtf is up? T_T Please help!

I get that from time to time with other settlements. Chances are there is a Synth you missed stuck in some hidden area. I have had them stuck in objects I have built, such as walls and concrete platforms.

If you get the quest complete mission and it is happening then I don't know what it could be. If you don't get that message then chances are you missed one.

Nope, not completed. In miscellaneous quests, still says "Help the castle." but I'll take apart everything to see if it's stuck in a concrete wall. However, wouldn't it show up on the map if I missed one?

Yes, not only are the attack mission entirely tiresome. They're also entirely broken. I had the same experience with Hangmans. I went there, fought a bunch of raiders, stayed for about three game days, since the mission wouldn't dissapear from my log and decided to move on. Only to get the good old failed to defend message and a lot of destruction at the settlement.

Damn it... my Minutemen have some good gear too... I don't want to sacrifice them and start repopulating Castle ... One thing that erk me... I have 3 cannons and six turrets along the wall, aimed at the two entrance ways to the fort.... yet they couldn't stop 7-10 synths before the go to the castle?

Even more screwed up, I didn't do anything to provoke the Institute. They were already on my [censored] list for killing my wife but now they attack my "Home". Yeah... despite their Xenophobia, I'm joining BoS and will wipe out the Institute... bastards Now it's personal...ish

One more pointer, I BELIEVE that

But that doesn't mean to kill them all.

Synths teleport inside settlements, along with any other enemies that simply spawn inside them anyway. Always have guns pointing inside your settlements too. Except for rockets, as their slash damage will kill friendlies.


Is there a way to test if you have a synth hiding in your settlement population?

Wait... settlers can be Synths? The settler that died had a Synth component on them... I saw it and was like "Oh HELL no, she was a Synth?" Then saw it was a settler I gave a sniper to, I simply thought she picked up the component...

Same with AK, they casn replace settlers?... I wonder if pickpocketing will help...

From what I have encountered if it is indeed stuck in some odd spot or in an object, the red marker doesn't show up on the map. Did you check the inside of the Castle in case one ran inside?

I have had a few times were I just gave up and let the settlement take damage. It doesn't take long to replace the stuff that is lost.

What I do with the Castle is I have all the possible was blocked off but for that one side entrance that is actually an entrance, not just those large breaks in the Wall. This makes it so all the attackers have to run into that one hallway to enter the Castle. I put turrets and such all along the top of the wall and some facing into to court yard in case some make it.

Yes, that happens. And if it does, it's yet another source for error in these attack missions. We're usually talking about one person here, yet the mission fails in most of the cases, since your settlers already killed the person in question before you arrive. The game however doesn't recognize that and hands a failure to you, weaving destruction in it's wake.

I haven't had this issue yet, I just recently got the first synth attack at Covenant which was already glitching out on me, but you might find the answer you're looking for in a similar thread I started:
http://www.gamesas.com/topic/1576764-failed-to-defend-settlements-where-synths-attack/

I think it may be a bug, not the fact that they are synths, but because they are almost ALWAYS dead before you get there and won't count toward your kill count. That is the main reason you will fail during a synth attack. I recently failed a attack on Sanctuary that i didn't even get notified for (non synth). I love settlement building and i love everything that has to do with settlements(aside from Preston Gravey) but i wish they would notify you some other way, and that being said i always have my radio tuned to Radio Freedom. How did i miss it?

Damn... I hate to sacrifice the Castle. However RP wise, aside from Nora's scripted death and Shaun, it gives reason to join BoS and destroy the institute.

Thanks for the help.

Load the game and try it again?

Tried, even saved slept for a day, nada. I had to let it go. Thankfully the only casualty was my crops, better then original. All but 5 people were killed. Anyways matter fixed. Thanks for your reply tho Ykchau.